Valve jet printers are used in industrial applications for the printing of large characters and pictures onto cartons or other large items. Unlike other drop on demand ink jet systems, the design of using a valve to control the printer nozzle enables highly volatile solvents such as MEK (methyl ethyl ketone) to be used, since there is a reduced requirement to prevent drying at the nozzle. The reason for the above is that the valve jet is purged with a solution prior to extended shutdown periods. Valve jet printers have less complex technology than ink jet printers and are capable of printing larger volumes of material and more material area in a given time and are generally less expensive.
Red fluorescent inks have been used in postage meters or franking machines for imprinting postal indicia. Inks used for the printing of postal indicia in the United States have to be red fluorescent so that automatic sorting equipment may be used by the United States Postal Service. The excitation wave length at 254 nm of a typical red fluorescent ink while the emission radiation is in the range of 580-40 nm. The image obtained with the red fluorescent inks has to be permanent, i.e. good water fastness less than 0.07 optical density background change, good smear fastness and light fastness i.e., minimal change in L, a, b values. Also, the images on various substrates have to be resistant to mechanical abrasion and common office chemicals. An ink that does not dry out at extreme temperature (50.degree. C.) is beneficial to the printing system. The ink that penetrates rapidly into different substrates and has minimal offset to overlapping envelopes is also beneficial to the printing system.
A facer canceller is a device for handling, authenticating and sorting randomly oriented letter mail. Facer cancellers check the top and bottom front and back of a mail piece to cancel the stamps thereon and determine if a postal indicia is present. Facer cancellers can also identify the presence or absence of a tagger mark on an envelope. A tagger mark may have any geometric shape as long as it supplies enough fluorescent intensity to be detected. The tagger mark containing fluorescence enables a facer canceller to read and orient the mail piece.
An ink jet printer is incapable of placing fluorescent tags on mail pieces at rates greater than or equal to four #10 mail pieces per second, while meeting all of the above requirements. A valve jet printer is capable of printing fluorescent tags on mail pieces at speeds equal to or greater than four #10 mail pieces per second. When current fluorescent inks are used in valve jet printers the ink bleeds when the printing surface is exposed to water. This creates a problem since water is used to seal the mail piece.
Another disadvantage of prior art fluorescent ink jet inks is that they are difficult to manufacture. The inks require high purity i.e., the insoluble salts contained in the dyes and toner of the fluorescent ink have to be lower than one part per billion is preferred. The reason for the above is that if the insoluble salts have a greater concentration than that specified above, there will be a residue build up on the nozzles of the ink jet printer, which will cause clogging of the nozzle.
Another problem of prior art fluorescent inks is that they do not give consistent print quality on a large variety of substrates. Tagger inks have to be used on a large variety of paper envelopes. The components of the paper can be inhibiting to the fluorescence intensity or can have adverse effects on the optical density of the prints. Therefore, there is a need for a tagger mark that will have consistent fluorescence and optical density on a large variety of envelopes, while interacting with the paper.
Another disadvantage of the prior art is that the dyes have to be purified to prevent coagulation in the nozzle or jets of printers. This causes erratic firing of the printer and degrades the life of the print head. Often times ions like sodium, chlorine, magnesium, and sulfates have to be removed to lower concentrations. Purification methods are expensive and time consuming.